Accidentally ate a tomato which was 15 days out of date should i be concerned?

I would not expect anything worrisome beyond the possibility of indigestion/diarrhea. It is just s poor source of nutrition after its expiration date.

If you did not have any symptoms in four hours after eating the suspect tomato, you are okay. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV vaccine. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/sa